1. Field of the Invention
The present invention relates to a semiconductor device as typified by a thin-film transistor formed on a substrate, as well as to a manufacturing method thereof.
2. Description of Related Art
The thin-film transistor using a silicon film is known. In this technique, a thin-film transistor is formed by using a silicon film formed on a glass or quartz substrate.
The reason for using a glass or quartz substrate is that thin-film transistors are used for an active matrix liquid crystal display device. Conventionally, thin-film transistors are formed by using an amorphous silicon film. However, to provide higher performance, it is now attempted to form thin-film transistors by using a silicon film having crystallinity (called a crystalline silicon film).
A thin-film transistor using a crystalline silicon film can operate faster than that using an amorphous silicon film by two or more orders. Therefore, by employing thin-film transistors using a crystalline silicon film, peripheral drivers circuits of an active matrix liquid crystal display device, which are conventionally external IC circuits, can be formed on a glass or quartz substrate with an active matrix circuit.
The above configuration is very advantageous in terms of miniaturization of the entire device and simplification of a manufacturing process as well as reduction in manufacturing cost.
A crystalline silicon film is obtained by forming an amorphous silicon film through plasma CVD or low-pressure thermal CVD, and then crystallizing it through a heat treatment or irradiation with laser light.
However, with the heat treatment, it is currently difficult to obtain a desired level of crystallinity over a wide area; for example, crystallization is uneven.
On the other hand, although the method using the laser light irradiation can provide superior crystallinity partially, it is difficult for even such a technique to provide good annealing effects over a wide area. In particular, irradiation with laser light under such conditions as to provide a high degree of crystallinity tends to be unstable.
A technique described in Japanese Unexamined Patent Publication No. Hei. 6-232059 is known as a method for solving the above problems. In this technique, a metal element (for instance, nickel) for accelerating crystallization of silicon is introducing an amorphous silicon film, thereby providing a crystalline silicon film by a heat treatment of a lower temperature than in conventional techniques.
Studies of the present inventors have proved that a crystalline silicon film produced by this technique has, over a wide area, sufficiently high crystallinity to be suitable for practical use.
However, this technique has a problem that delicate control is needed for the introduction amount of a metal element because it remains in a resulting film. Accordingly, it has been found that this technique is problematic in reproducibility and(electrical stability of a device produced.
In addition, there is a problem that the characteristics of a semiconductor device produced considerably varies with time, which is an influence of a residual metal element. The residual metal element also causes a problem that the off-current of a thin-film transistor fabricated by using the above-mentioned film is large.
That is, although the metal element for accelerating crystallization of silicon is very useful to form a crystalline silicon film, it is associated with negative factors that cause various problems after formation of a crystalline silicon film.
An object of the present invention is to provide a technique for reducing the concentration of a metal element for accelerating crystallization of silicon in a crystalline silicon film formed by utilizing the metal element. Another object of the invention is to provide a thin film semiconductor device having superior electrical characteristics by utilizing the film formed in the present invention.
According to one aspect of the invention, there is provided a manufacturing method of a semiconductor device, comprising the step of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon, wherein during the step, a maximum process temperature (the highest temperature during the process) is higher than 650xc2x0 C. and lower than 1,000xc2x0 C., and a process time not shorter than one hour; the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650xc2x0-1,000xc2x0 C.
According to another aspect of the invention,there is provided a manufacturing method of a semiconductor device, comprising the step of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon, wherein during the step, a maximum process temperature be higher than 700xc2x0 C. and lower than 980xc2x0 C. and a process time be not shorter than 30 minutes.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device, comprising the steps of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon; and removing the metal element from the crystalline silicon film by forming a thermal oxidation film containing a halogen element, wherein each of the two steps has a maximum process temperature that is higher than 650xc2x0 C. and lower than 1,000xc2x0 C., and a process time not shorter than one hour; the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650xc2x0-1,000xc2x0 C.
According to a further aspect of the invention, there is provided a semiconductor device using a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650xc2x0-1,000xc2x0 C.
According to another aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; the substrate has a strain point of 650xc2x0-1,000xc2x0 C.; the silicon thin film contains a metal element that accelerates crystallization of silicon at a concentration of 1xc3x971016 to 5xc3x971019 cmxe2x88x923, the metal element existing at a high concentration in the vicinity of a interface of the silicon thin film.
Where a metal element for accelerating crystallization of silicon is used, the concentration of the residual metal element in a resulting crystalline silicon film is within the above range. If a crystalline silicon film contains a metal element at a higher concentration than the above range, it is too much influenced by the metal element to exhibit semiconductor characteristics. Further, the reliability of a semiconductor device is extremely lowered.
According to still another aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; the substrate has a strain point of 650xc2x0-1,000xc2x0 C.; the silicon thin film contains a metal element that accelerates crystallization of silicon at 1xc3x971016 to 5xc3x971019 cmxe2x88x923, and a halogen element at not less than 1xc3x971016 cmxe2x88x923.
Where a thermal oxidation film is formed by a heat treatment in an atmosphere containing a halogen element, the halogen element enters into a crystalline silicon film during the formation of the thermal oxidation film. As a result, the halogen element is contained in the crystalline silicon film at not less than 1xc3x971016 cmxe2x88x923. It is preferred that the upper limit of the concentration of the halogen element be about 5xc3x971020 cmxe2x88x923.
According to a further aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate has a strain point of 650xc2x0-1,000xc2x0 C.; and the silicon thin film contains a metal element that accelerates crystallization of silicon at 1xc3x971016 to 5xc3x971019 cmxe2x88x923, and a halogen element at not less than 1xc3x971016 cmxe2x88x923.
In the invention, the metal element may be one or a plurality of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.
The oxidizing atmosphere containing a halogen element may be an O2 atmosphere or an O2-containing atmosphere to which one or a plurality of gases selected from HCl, HF, HBr, Cl2, F2, Br2, and NF3 are added.
In this specification, the impurity concentration is defined as the minimum of measurement values of SIMS (secondary ion mass spectrometry), OH group is measured by IR-Spectrometer, and Chlorine is measured by Radioactive Analysis.